function out=fitLorentzian1peak(Param,x)
A1=Param(1);
W1=Param(2);
X1=Param(3);
bkg_a=Param(4);
bkg_b=Param(5);

out=(bkg_a*x+bkg_b)+A1./(1+((x-X1)/W1).^2);
